This invention relates to scanning probe microscopes and, more particularly, to a method of operation thereof in order to increase the image-taking speed of the device. Scanning probe microscopes, such as the scanning tunneling microscope and the atomic force microscope, operate by scanning a probe over a surface in which the probe is very close to the surface or contacts the surface very lightly. In a scanning tunneling microscope, the tip is at a distance of just a few atoms from the surface in order for a tunneling current to flow the probe tip to the surface. The tunneling current is used in a feedback system which regulates the vertical height of the probe to keep the current, and therefore the distance of the probe from the surface, constant. In an atomic force microscope, the tip is mounted on a bendable arm which is instrumented such that bending of the arm can be measured in order to obtain the force acting on the tip. This force can be one which attracts the tip to the surface, such as a Van der Waals force, or a magnetic field force or replulsive force, when the tip is in contact with the surface. This force is typically used in feedback system to regulate the height of the probe or sample to keep the force constant during the scan. Other probes which have been used include thermal probes, electric field probes, and light probes.
As the field of scanning probe microscopes has expanded, the need for very large scans (and corresponding implementation thereof) has increased, in turn slowing down the time it takes to acquire an image because of the large area that must be covered with the tip close to the surface. The inventors herein, for instance, have made scanners for a scanning tunneling microscope which can scan over a 90 by 90 micron area. In prior co-pending application serial number 361,545, filed 5 June 1989 by Virgil Elings and John Gurley entitled JUMPING PROBE MICROSCOPE, assigned to the common assignee of this invention, one approach to help speed up these large scans is shown. This application is directed to yet another approach to increasing the scanning rate of scanning probe microscopes.
In all scanning probe microscopes, the probe is moved in a raster scan, back and forth in X as the probe moves slowly in Y, the perpendicular direction, with the feedback systems always operating to control Z, the vertical direction; otherwise, the probe would strike the surface. Data is taken only in one direction in X. Because of the hysteresis in the scanners, the data in the two directions does not agree exactly and therefore cannot be used to make a single image. The tip cannot be moved more quickly in the direction in which the data is not used since the probe is already moving as fast as it can without hitting the surface and damaging the probe.
Wherefore, it is the object of this invention to provide a method of operation with standard scanning probe microscopes which will decrease the time required to complete a total scan of a surface and ontain data therefrom.
Other objects and benefits of the invention will become apparent from the detailed description which flows herein after when taken with the drawing figures which accompany it.